Extension Lead Load Calculator
High-draw appliances like kettles, heaters and hairdryers can add up quickly on a single extension lead, and it's easy to underestimate the combined load. List what you're planning to plug in below and we'll check the total against your lead's safe rating.
Check your extension lead load
List what you want to plug in and we'll check it against your lead's safe rating.
Total load: 4,200W of a safe maximum of 2,990W on a 13a lead (standard uk)
Overloaded by 1,210W — split these across more than one lead/socket.
Recommended products
A few well-reviewed extension leads and electrical accessories.
£3.69
Pros
- Cheap way to confirm a socket or fitting is dead before working on it
- Slim pocket size for a tool bag or van door pocket
- Detects both live and neutral wires
Cons
- Neon indicator can be hard to see in bright daylight
£8.99
Pros
- Trusted UK brand fitted as standard by many electricians
- Inherent antimicrobial properties on the faceplate
- Neat white moulded finish matches most existing sockets
Cons
- Must be fitted by, or notified to, a qualified electrician under Part P
Currently unavailable
Pros
- Combined breaker and RCD protection on a single circuit
- Compatible with Schneider Resi9 consumer units
- Reduces nuisance tripping compared with a shared RCD
Cons
- Installation must be carried out by a registered electrician
Frequently asked questions
What happens if I overload an extension lead?
An overloaded lead carries more current than it is rated for, causing the cable to heat up. This can trip a circuit breaker as a safety measure, but sustained overloading — especially on a coiled or covered lead — is a genuine fire risk.
What is a standard UK extension lead rated at?
Most household extension leads are rated at 13A, matching a standard UK plug, which gives a safe maximum of around 3000W (13A × 230V). Heavy-duty or site/trade leads are often rated at 16A for higher-draw equipment.
Should I always uncoil an extension lead before use?
Yes — a coiled lead traps heat and can overheat even well within its rated wattage, particularly with high-draw appliances like heaters or kettles. Always run the lead out fully before use.
Can I plug an extension lead into another extension lead?
Daisy-chaining extension leads is not recommended. It makes it easy to unknowingly exceed the rating of the weakest lead in the chain and increases the risk of a loose or overheating connection.
How this calculator works
The calculator takes the total wattage (or kilowatt hours – kWh) of all appliances you plan to connect to an extension lead as input. Wattage is a measure of how much electricity an appliance consumes per hour, usually displayed in watts or kilowatts. The calculator then divides this total wattage by the extension lead’s amp rating (measured in Amps - A). This calculation determines whether the lead can safely supply the required current without overheating and potentially causing a fire.
It’s important to note that this calculator assumes each appliance operates at its full rated power. In reality, appliances rarely run continuously at their maximum wattage. However, for quick safety checks, it provides a conservative estimate based on peak usage. The calculator also assumes a standard UK voltage of 230V.
Typical Appliance Wattage Comparison (UK)
| Appliance | Wattage Range |
|---|---|
| LED Bulb (Standard) | 9-15W |
| Light Bulb (Incandescent) | 60W |
| Laptop Computer | 30-75W |
| Mobile Phone Charger | 5W |
| Toaster | 800-1200W |
| Microwave Oven | 900-1800W |
| Electric Fire (Ceramic) | 1500-3000W |
| Heater (Fan) – Small Room | 1400-2000W |
| Kitchen Mixer/Blender | 600-1000W |
| TV (LED LCD) | 80-200W |
Worked example: Calculating Load on a 16A Extension Lead
Let’s say you want to plug the following into a standard 16 Amp (1.6kW) extension lead: a small ceramic heater (1500W), a laptop charger (60W), and a mobile phone charger (5W). Adding these together, the total wattage is 1500 + 60 + 5 = 1565 Watts. Now, we divide this by the extension lead’s amp rating: 1565 / 1.6 = 978.125 Amps. This result shows that the calculated amperage exceeds the 1.6A limit of the extension lead.
Because the calculation returns a value greater than 1.6A, this indicates the extension lead is overloaded. Using an extension lead with a lower amp rating (e.g., 10A) or choosing appliances with a lower wattage would be necessary to safely operate these devices simultaneously.
More questions answered
What does the result of the calculation mean?
The result indicates whether you’re exceeding the safe current limit of the extension lead. A value greater than the amp rating signifies overloading, which can overheat the lead and potentially cause a fire. A value below the rating is generally considered safe, but always err on the side of caution.
What if I want to plug in more appliances?
Simply add up the wattage (or kWh) of all devices you intend to use. If the total exceeds the extension lead’s amp rating, you'll need a higher-rated lead or fewer devices. It’s always better to overestimate than underestimate.
Can I use this calculator with multiple extension leads?
No, this calculator is designed for a single extension lead. To calculate the total load across multiple leads, you'd need to sum the wattage of all appliances plugged into *each* lead. This can quickly become complex.
What if an appliance’s wattage fluctuates?
This calculator assumes continuous operation at the appliance’s rated wattage. Fluctuations in power consumption (e.g., a hairdryer cycling on and off) will slightly overestimate the load, but it's still a useful safety check.
Are there any appliances I shouldn't include in this calculation?
Generally, you should include all electrical devices that will be plugged into the extension lead. However, some specialized equipment (like industrial machinery) may have very high power requirements and could significantly overload a standard extension lead.
What happens if the calculator gives me a negative result?
A negative result isn’t possible with this calculation. It indicates that your appliances use less power than the lead can supply, which is perfectly safe. However, it doesn’t guarantee the lead is suitable for all applications – consider its length and condition.
I'm using a portable heater - how does that affect the calculation?
Portable heaters often have high wattage ratings (upwards of 2000W). Be particularly cautious when using them on extension leads, as they can quickly overload even higher-rated leads. Always check the heater’s wattage and ensure it's well below the lead’s rating.
Can I use this calculator to determine if an appliance is suitable for a specific extension lead?
Yes! The calculator helps you assess whether your chosen extension lead can handle the power demands of the appliances you intend to plug into it. Select the appliances and input their wattage to see if they're compatible.
What’s the difference between watts and amps?
Watts measure electrical *power* (how much energy is used). Amps measure electrical *current* (the flow of electrons). The calculator uses wattage to determine the total load, then converts it to amps using Ohm's Law (Wattage = Voltage x Current) – a simplified version for this calculation.
What if my extension lead is damaged?
If you notice any signs of damage to your extension lead – such as frayed wires, cracked insulation or unusual smells – immediately disconnect it from the mains and dispose of it safely. Do not attempt to use a damaged extension lead; this calculator only assesses safe loading for undamaged leads.